#define TIF_SINGLESTEP 4 /* reenable singlestep on user return*/
#define TIF_SSBD 5 /* Speculative store bypass disable */
#define TIF_SPEC_IB 9 /* Indirect branch speculation mitigation */
+#define TIF_SPEC_L1D_FLUSH 10 /* Flush L1D on mm switches (processes) */
#define TIF_USER_RETURN_NOTIFY 11 /* notify kernel of userspace return */
#define TIF_UPROBE 12 /* breakpointed or singlestepping */
#define TIF_PATCH_PENDING 13 /* pending live patching update */
#define _TIF_SINGLESTEP (1 << TIF_SINGLESTEP)
#define _TIF_SSBD (1 << TIF_SSBD)
#define _TIF_SPEC_IB (1 << TIF_SPEC_IB)
+#define _TIF_SPEC_L1D_FLUSH (1 << TIF_SPEC_L1D_FLUSH)
#define _TIF_USER_RETURN_NOTIFY (1 << TIF_USER_RETURN_NOTIFY)
#define _TIF_UPROBE (1 << TIF_UPROBE)
#define _TIF_PATCH_PENDING (1 << TIF_PATCH_PENDING)
static void __init mds_print_mitigation(void);
static void __init taa_select_mitigation(void);
static void __init srbds_select_mitigation(void);
+static void __init l1d_flush_select_mitigation(void);
/* The base value of the SPEC_CTRL MSR that always has to be preserved. */
u64 x86_spec_ctrl_base;
DEFINE_STATIC_KEY_FALSE(mds_idle_clear);
EXPORT_SYMBOL_GPL(mds_idle_clear);
+/*
+ * Controls whether l1d flush based mitigations are enabled,
+ * based on hw features and admin setting via boot parameter
+ * defaults to false
+ */
+DEFINE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush);
+
void __init check_bugs(void)
{
identify_boot_cpu();
mds_select_mitigation();
taa_select_mitigation();
srbds_select_mitigation();
+ l1d_flush_select_mitigation();
/*
* As MDS and TAA mitigations are inter-related, print MDS
}
early_param("srbds", srbds_parse_cmdline);
+#undef pr_fmt
+#define pr_fmt(fmt) "L1D Flush : " fmt
+
+enum l1d_flush_mitigations {
+ L1D_FLUSH_OFF = 0,
+ L1D_FLUSH_ON,
+};
+
+static enum l1d_flush_mitigations l1d_flush_mitigation __initdata = L1D_FLUSH_OFF;
+
+static void __init l1d_flush_select_mitigation(void)
+{
+ if (!l1d_flush_mitigation || !boot_cpu_has(X86_FEATURE_FLUSH_L1D))
+ return;
+
+ static_branch_enable(&switch_mm_cond_l1d_flush);
+ pr_info("Conditional flush on switch_mm() enabled\n");
+}
+
+static int __init l1d_flush_parse_cmdline(char *str)
+{
+ if (!strcmp(str, "on"))
+ l1d_flush_mitigation = L1D_FLUSH_ON;
+
+ return 0;
+}
+early_param("l1d_flush", l1d_flush_parse_cmdline);
+
#undef pr_fmt
#define pr_fmt(fmt) "Spectre V1 : " fmt
#include <linux/export.h>
#include <linux/cpu.h>
#include <linux/debugfs.h>
+#include <linux/sched/smt.h>
#include <asm/tlbflush.h>
#include <asm/mmu_context.h>
#include <asm/nospec-branch.h>
#include <asm/cache.h>
+#include <asm/cacheflush.h>
#include <asm/apic.h>
#include <asm/perf_event.h>
*/
/*
- * Bits to mangle the TIF_SPEC_IB state into the mm pointer which is
+ * Bits to mangle the TIF_SPEC_* state into the mm pointer which is
* stored in cpu_tlb_state.last_user_mm_spec.
*/
#define LAST_USER_MM_IBPB 0x1UL
-#define LAST_USER_MM_SPEC_MASK (LAST_USER_MM_IBPB)
+#define LAST_USER_MM_L1D_FLUSH 0x2UL
+#define LAST_USER_MM_SPEC_MASK (LAST_USER_MM_IBPB | LAST_USER_MM_L1D_FLUSH)
/* Bits to set when tlbstate and flush is (re)initialized */
#define LAST_USER_MM_INIT LAST_USER_MM_IBPB
local_irq_restore(flags);
}
+/*
+ * Invoked from return to user/guest by a task that opted-in to L1D
+ * flushing but ended up running on an SMT enabled core due to wrong
+ * affinity settings or CPU hotplug. This is part of the paranoid L1D flush
+ * contract which this task requested.
+ */
+static void l1d_flush_force_sigbus(struct callback_head *ch)
+{
+ force_sig(SIGBUS);
+}
+
+static void l1d_flush_evaluate(unsigned long prev_mm, unsigned long next_mm,
+ struct task_struct *next)
+{
+ /* Flush L1D if the outgoing task requests it */
+ if (prev_mm & LAST_USER_MM_L1D_FLUSH)
+ wrmsrl(MSR_IA32_FLUSH_CMD, L1D_FLUSH);
+
+ /* Check whether the incoming task opted in for L1D flush */
+ if (likely(!(next_mm & LAST_USER_MM_L1D_FLUSH)))
+ return;
+
+ /*
+ * Validate that it is not running on an SMT sibling as this would
+ * make the excercise pointless because the siblings share L1D. If
+ * it runs on a SMT sibling, notify it with SIGBUS on return to
+ * user/guest
+ */
+ if (this_cpu_read(cpu_info.smt_active)) {
+ clear_ti_thread_flag(&next->thread_info, TIF_SPEC_L1D_FLUSH);
+ next->l1d_flush_kill.func = l1d_flush_force_sigbus;
+ task_work_add(next, &next->l1d_flush_kill, TWA_RESUME);
+ }
+}
+
static unsigned long mm_mangle_tif_spec_bits(struct task_struct *next)
{
unsigned long next_tif = task_thread_info(next)->flags;
unsigned long spec_bits = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_SPEC_MASK;
+ /*
+ * Ensure that the bit shift above works as expected and the two flags
+ * end up in bit 0 and 1.
+ */
+ BUILD_BUG_ON(TIF_SPEC_L1D_FLUSH != TIF_SPEC_IB + 1);
+
return (unsigned long)next->mm | spec_bits;
}
indirect_branch_prediction_barrier();
}
+ if (static_branch_unlikely(&switch_mm_cond_l1d_flush)) {
+ /*
+ * Flush L1D when the outgoing task requested it and/or
+ * check whether the incoming task requested L1D flushing
+ * and ended up on an SMT sibling.
+ */
+ if (unlikely((prev_mm | next_mm) & LAST_USER_MM_L1D_FLUSH))
+ l1d_flush_evaluate(prev_mm, next_mm, next);
+ }
+
this_cpu_write(cpu_tlbstate.last_user_mm_spec, next_mm);
}